Soil vapor extraction test in a radiologically contaminated site, Hanford site

A pilot test was conducted at the Hanford site in Washington State using soil vapor extraction technology, to test the vapor extraction technology under Hanford Site conditions, and to provide data for designing a large-scale vapor extraction system that will be used to stabilize an existing vadose zone CCl4 vapor plume. Testing was performed at the 216-Z-1-A tile field where over 5 million liters of water, 245 metric tons of CCl4, and 58 kilograms of plutonium and americium were disposed in the 1960s. The test objectives were to determine the distribution of CCl4 beneath the tile field, estimate soil permeabilities, observe trends in CCl4 concentrations during soil vapor extraction, and determine the behavior of radionuclides during the extraction process. The presence of the radionuclides required the use of a high-efficiency particulate filter mounded in-line with the conventional vapor extraction equipment. Gas and filter samples were collected for laboratory analysis using a gas chromatograph/mass spectrometer. Real-time monitoring was performed using on-fine flame-ionization and photo-ionization detectors for CCl4, and continuous alpha-radiation and beta-radiation air monitors for radionuclides. The test results showed that CCl4 concentrations generally increased with depth with significant concentrations of CCl4 detected outside the tile field boundaries; air permeabilities were in the range of a sand; large amounts of CCl4 were produced (over 365 lbs for the 80 hour test at concentrations up to 900 ppmv); plutonium and americium were not detected during the test or later on any of the test equipment; and unexpectedly high volumes of radon can be produced. The test demonstrated that the soil vapor technology is a viable method for removing CCl4 at the tile field, with the ability to separate CCl4 from the plutonium and americium soil contamination